Under WCU Library Resources, I provided tips for finding memoirs, letters, diaries, etc. in our own collections. By using some other tools, you could locate even more, plus a huge range of books on almost any topic simply published during the war. Here are 3 tools you could use.
1) Google books
Because you can limit your search to a specific publication date period, google books can be a fantastic way to find older books to use as primary resources. See the video below for how to set up a search.
2) HathiTrust
HathiTrust specializes in digitized books. Like Google Gooks, it is of more limited use for WW II, as most non-government publications from the period are still covered by copyright. But it is my go to place to see if an older book has been digitized. Remember, if a book hasn't been digitized, there is still a very good chance we can get a copy through Interlibrary Loan.
Tip: HathiTrust's search is set to search Full Text of all books. In most cases, it is better to do a Catalog search instead, which will search the catalog record, including titles and subject headings, but not the full text. "Full View Only" means only searching books where a digital copy is freely available.
3) WorldCat.org
WorldCat.org is the best book for looking for additional book-length memoirs, letters, diaries, etc. Use the same techniques as discussed for our catalog. You can also set a date range to look for older books, but the lack of previews makes it a bit less useful than Google Books.
Professor Kirscehnbaum's D2L course page on Research Resources has a ton of great websites and digital collections. Rather than trying to recreate what she has already done, I have just added a few sources or offered some additional tips on using some of those sites and collections.
The Library of Congress has many fantastic digital collections, but it can be difficult to find relevant ones, because their interface doesn't allow for sorting by date. I've pulled out a few collections that I think best relate to your class topic, but there are almost certainly more that I've missed! For all of them, once you are in a specific collection, you can limit by date in the left hand column, first by century (1900-1999), then by decade. You might need to look at both 1930-1939 and 1940-1949.